The present invention relates to a cylindrical color filter driver for an optical reader which utilizes a motor to rotate a cylindrical color filter assembly for permitting the color image of a document to be reproduced through a single color charge coupled device.
Various color filter drivers are known and widely used in color readers. These color filter drivers include rotary wheel type color filter drivers, sector disk type color filter drivers and linear color filter drivers. However, these color filter drivers are still not satisfactory in function. FIG. 1 illustrates a rotary wheel type of color filter driver in which the color wheel which is referenced as 10 has red, blue and green color filters 1a,1b,1c and a transparent window 1d arranged around a circle, the top cover which is referenced as 2 has two LEDs (light emitting diodes) 3a, 3b respectively aligned with two photo detectors 4a,4b. Rotating the color wheel 10 causes light holes 6a,6b,6c to be respectively aligned with one LED 3b and one photo detector 4b at different times. Output signals of the photo detectors 4a,4b are transmitted to a signal processor so as to provide a respective start signal for each scanning and a respective start signal for red, green and blue scanning mode. This structure of color filter driver is expensive to manufacture, requires much installation space and provides low resolution performance. Because the red, blue and green color filters provide different light transmission rates, the charged couple device will be exposed to the different intensity of light during a continuous scanning of the primary colors, and therefore the signal data processing technique becomes complicated. Furthermore, executing a synchronizing control takes much time, and therefore the scanning speed can be not improved. FIG. 2 illustrates a sector disk type color filter driver. This structure of sector color filter driver still requires much installation space. Because it utilizes a reversible motor to alternatively rotate the sector color filter assembly back and forth, the cost of the motor is expensive, and the operation of the motor is difficult to control accurately. Furthermore, the scanning speed can not be improved because the sector color filter assembly is driven to make a reciprocating motion. FIG. 3 illustrates a linear color filter driver which utilizes a reversible motor to alternatively move a color filter assembly back and forth through a linear source. This structure of linear color filter driver is inexpensive to manufacture and requires much installation space. The reciprocating motion of the color filter assembly can not improve the scanning speed.